Initiator composition and method for anionic polymerisation

ABSTRACT

The invention relates to an initiator composition for anionic polymerization, comprising at least one alkali metal hydride selected from LiH, NaH, and KH, and at least one organylaluminum compound, and to a process for the anionic polymerization of styrene monomers or of diene monomers using the initiator composition.

The invention relates to an initiator composition for anionicpolymerization, comprising at least one alkali metal hydride selectedfrom LiH, NaH, and KH, and at least one organylaluminum compound.

The invention further relates to a process for preparing the initiatorcomposition, and to a process for the anionic homo- or copolymerizationof styrene monomers or of diene monomers in the presence of theinitiator composition, and also to the use of the initiator compositionfor preparing polymers. Finally, the invention relates to the polymersobtainable by the process, to the use of these for producing moldings,films, fibers, or foams, and to the moldings, films, fibers, and foamsmade from the polymers.

Anionic polymerization generally proceeds very rapidly, and theconsiderable amount of heat generated makes control difficult on anindustrial scale. If the polymerization temperature is lowered, theresult is an excessive rise in viscosity, in particular for concentratedsolutions. Reducing the initiator concentration increases the molecularweight of the polymer formed. Control of the reaction via appropriatedilution of the monomers leads to higher requirement for solvent and tolow space-time yields.

Various additives to the anionic polymerization initiators, affectingpolymerization rate, have therefore been proposed.

The effect of Lewis acids and Lewis bases on the rate of anionicpolymerization of styrene has been reported in Welch, Journal of theAmerican Chemical Society, Vol. 82 (1960), pp. 6000-6005. Here it wasfound that small amounts of Lewis bases, such as ethers and amines,accelerate the n-butyllithium-initiated polymerization of styrene at 30°C. in benzene, whereas Lewis acids, such as alkylzinc and alkylaluminumcompounds reduce the polymerization rate or, if used in more thanstoichiometric amounts, stop the polymerization.

U.S. Pat. No. 3,655,790 describes organomagnesium-alkali metal hydridecomplexes M_(n)MgR¹R²H_(n) where M=Na, K, Li, Cs; R¹ and R²=C₃₋₁₅-alkyl,-aryl, -aralkyl; n=½, 1, 2, 3, and their use as reducing agents andmetallizing agents.

U.S. Pat. Nos. 3,691,241 and 3,817,955 disclose a process for thepolymerization of various monomers, including butadiene, isoprene, andstyrene, using the organomagnesium-alkali metal hydride complexesdescribed in U.S. Pat. No. 3,655,790.

A difference from the metal complexes disclosed above is that neithermagnesium nor organylmagnesium compounds is present in the initiatorcompositions of the invention.

DE-A 19806772 discloses initiator compositions made from an organylalkali metal compound (i.e. alkyl, aryl, aralkyl alkali metal compound),e.g. sec-butyllithium, and from an organylaluminum compound, e.g.triisobutylaluminum (TIBA), and their use for the polymerization ofvinylaromatics and dienes.

U.S. Pat. No. 3,716,495 teaches initiator compositions made from a)organolithium compounds RLi_(x) where R=C₁₋₂₀-alkyl, -aryl, -cycloalkyl,-alkaryl, or -aralkyl, for example n- or sec-butyllithium, b)organylmetal compounds R_(n)M, where R is as defined above and M=a metalfrom the groups 2a (alkaline earth metals), 2b (zinc group), and 3a(boron group), e.g. diethylzinc or organylaluminum compounds, and c)polar compounds, such as tetrahydrofuran (THF). They are used for thepolymerization of dienes and vinylaromatics.

A disadvantage of the use of initiators which comprise organolithiumcompounds (organyllithium compounds), for example n-, sec-, ortert-butyllithium, is the high price of the organyllithium compounds,which makes the final polymer product more expensive.

A difference from the two initiator compositions disclosed above is thatthe initiators of the invention comprise alkali metal hydrides withoutorganyl radicals.

WO-A 98/07765 discloses initiators for anionic polymerization,comprising the organylmetal compounds

-   R¹M¹ where M¹=Li, Na, K    -   R¹=hydrogen, C₁₋₁₀-alkyl, C₆₋₂₀-aryl, C₇₋₂₀-alkyl substituted        aryl, and-   R² _(n)M² where M²=n-valent element of groups 2a, 2b, or 3a of the    Periodic Table,    -   R²=hydrogen, halogen, C₁₋₂₀-alkyl, C₆₋₂₀-aryl.

A corresponding polymerization process for styrene monomers or dienemonomers is also disclosed.

The present invention is a selection invention with respect to WO-A98/07765, in that hydrogen alone has been selected for R¹ and aluminumalone has been selected for M².

It is an object of the present invention to provide alternate initiatorcompositions for anionic polymerization (in particular of styrenemonomers or diene monomers). An alternate anionic polymerization processfor styrenes and dienes was also to be provided. The initiatorcompositions and the process were to have better cost-effectiveness thanthe processes of the prior art.

We have found that this object is achieved by means of the initiatorcompositions, processes, and uses mentioned at the outset. Theabovementioned polymers and their use have also been found, as have themoldings, films, fibers, and foams.

Preferred embodiments of the invention are given in the subclaims.

The initiator composition of the invention comprises at least one alkalimetal hydride selected from lithium hydride LiH, sodium hydride NaH, andpotassium hydride KH, and at least one organylaluminum compound(organoaluminum compound).

It is possible that the alkali metal hydride acts as initiator foranionic polymerization, e.g. of styrene monomers, insofar as it ispresent in solution in the solvent (usually non-polar, inerthydrocarbons). The organylaluminum compound improves the solubility ofthe alkali metal hydride in the solvent, possibly by complexing, andthus improves the activity of the alkali metal hydride. In addition, theAl organyl compound slows the rate of polymerization of the monomers(“retarder” action).

The alkali metal hydrides may be prepared in a known manner from thecorresponding metals and gaseous hydrogen at superatmospheric pressureand elevated temperature. However, they are also available in thechemicals market, for example in the form of pure solid or a suspendedin a solvent.

The amount needed of alkali metal hydride depends inter alia on thedesired molecular weight (molar mass) of the polymer to be prepared, onthe type and amount of organylaluminum compounds used, and on thepolymerization temperature. The amount used is generally from 0.0001 to10 mol %, preferably from 0.001 to 1 mol %, and particularly preferablyfrom 0.01 to 0.2 mol %, of alkali metal hydride, based on the totalamount of monomers used.

Organylaluminum compounds which may be used are monoorganyl compoundsRH₂Al, diorganyl compounds R₂HAl, and —preferably—triorganyl compoundsR₃Al. These radicals R may be identical or different and eachindependently of one another is hydrogen, halogen, C₁-C₂₀-alkyl,C₆-C₂₀-aryl, or C₇-C₂₀-alkyl-substituted aryl. Preferred organylaluminumcompounds are the trialkylaluminum compounds, such as triethylaluminum,triisobutylaluminum, tri-n-butylaluminum, triisopropylaluminum,tri-n-hexylaluminum. It is particularly preferable to usetriisobutylaluminum (TIBA).

The organylaluminum compounds used may also be those produced by partialor complete hydrolysis, alcoholysis, aminolysis, or oxidation of alkyl-or arylaluminum compounds, or those which bear alcoholate, thiolate,amide, imide, or phosphide groups. Examples arediethylaluminum(N,N-dibutylamide), diethylaluminum ethoxide,diisobutylaluminum ethoxide,diisobutyl-(2,6-di-tert-butyl-4-methylphenoxy)aluminum (CAS No.56252-56-3), methylaluminoxane, isobutylated methylaluminoxane,isobutylaluminoxane, tetraisobutyldialuminoxane, andbis(diisobutyl)aluminum oxide.

The organylaluminum compounds are obtainable in a manner known per se ormay be purchased in the form of commercially available products.

The amount needed of organylaluminum compound depends inter alia on thetype and amount of alkali metal hydrides used, and on the polymerizationtemperature. The amount used is usually from 0.0001 to 10 mol %,preferably from 0.001 to 1 mol %, and particularly preferably from 0.01to 0.2 mol %, of organylaluminum compound, based on the total amount ofmonomers used.

The molar ratio of alkali metal hydride (initiator) to organylaluminumcompound (retarder) may vary within wide limits.

It depends, for example, on the desired retardant action, thepolymerization temperature, the nature and amount (concentration) of themonomers used, and the desired molecular weight of the polymer.

It is useful to express the molar ratio mentioned as a molar ratio ofaluminum to alkali metal, Al/Li or Al/Na, or Al/K. In one preferredembodiment it is from 0.01:1 to 5:1, particularly preferably from 0.1:1to 2:1, and in particular from 0.5:1 to 1:1.

To prepare the initiator composition, it is usual to mix the alkalimetal hydride and the organylaluminum compound, preferably withconcomitant use of a solvent or suspension medium (depending on thesolubility of the alkali metal hydride or of the organylaluminumcompound, the term solvent being used below for brevity).

Particularly suitable solvents are inert hydrocarbons, more specificallyaliphatic, cycloaliphatic, or aromatic hydrocarbons, such ascyclohexane, methylcyclohexane, pentane, hexane, heptane, isooctane,benzene, toluene, xylene, ethylbenzene, decalin, or paraffin oil, or amixture of these. Toluene is particularly preferred.

In one preferred embodiment, the alkali metal hydride is used as itstands, i.e. as a dry solid. In another preferred embodiment, theorganylaluminum compound is used in solution in an inert hydrocarbon,e.g. toluene.

The temperature during the preparation of the initiator compositiondepends on the concentration, on the nature of the metal compounds, andon the solvent. The entire temperature range between the freezing pointand boiling point of the mixture is usually suitable. It is advantageousto operate in the range from 0 to 250° C., preferably in the range from20 to 200° C.

The holding or aging of the freshly prepared initiator composition isimportant for reproducible use in anionic polymerization. Experimentshave shown that initiator components which are used separately from oneanother or are mixed only briefly prior to the initiation of thepolymerization bring about polymerization conditions and polymerproperties which have poor reproducibility. The aging process observedis probably attributable to complexing of the metal compounds, whichproceeds more slowly that the mixing procedure.

An aging time of about 2 minutes is generally sufficient for the rangeof concentration and temperature given above. The homogeneous mixture ispreferably allowed to age for at least 5 minutes, in particular at least20 minutes. However, if the homogeneous mixture is allowed to age for anumber of hours, e.g. from 1 to 480 hours, this again does not generallyhave an adverse effect.

Another possibility is that styrene is also added to the initiatorcomposition. In this case the result is an oligomeric polystyryl anionhaving the organyl metal compounds complexed at its chain end. It ispreferable to use amounts of styrene in the range from 10 to 1000 mol %,based on the alkali metal hydride.

The initiator components may be mixed in any mixing assembly, preferablyin those which can be charged with an inert gas. Examples of suitableassemblies are stirred reactors with an anchor stirrer or vibratingvessels. Heatable tubes with static mixing elements are particularlysuitable for continuous preparation. The mixing procedure is needed forhomogeneous mixing of the initiator components. Mixing can, but neednot, continue while the mixture is allowed to age. The mixture may alsobe allowed to age in a stirred tank through which materials flowcontinuously, or in a tube section, the volume of which together withthe throughput rate determines the aging time.

The invention therefore also provides a process for preparing aninitiator composition comprising at least one alkali metal hydrideselected from LiH, NaH, and KH, and at least one organylaluminumcompound, where the alkali metal hydride and the organylaluminumcompound suspended or dissolved in an inert hydrocarbon are mixed andthe mixture is aged at from 0 to 120° C. for at least 2 minutes.

The invention also provides a process for the anionic homo- orcopolymerization of styrene monomers or of diene monomers or mixtures ofthese in the presence of an initiator composition, where the initiatorcomposition comprises at least one alkali metal hydride selected fromLiH, NaH, and KH, and at least one organylaluminum compound. This istherefore a process in which the initiator composition of the inventionis used.

Suitable styrene monomers are any of the vinylaromatic monomers, e.g.styrene, p-methylstyrene, p-tert-butylstyrene, ethylstyrene,vinylstyrene, vinylnaphthalene, and 1,1-diphenylethylene. It ispreferable to use styrene.

Examples of diene monomers which may be used are 1,3-butadiene,2,3-dimethylbutadiene, 1,3-pentadiene, 1,3-hexadiene, isoprene, andpiperylene. 1,3-Butadiene and isoprene are preferred, in particular1,3-butadiene (the abbreviated name butadiene being used below). It isadvantageous for the monomers used to have the purity typically requiredfor the process, i.e. troublesome impurities such as residual moisture,polar substances, and oxygen are removed immediately prior topolymerization in a manner known per se.

Use may be made of one type of monomer or of two or more types ofmonomers, i.e. the process is suitable for homopolymerization and forcopolymerization.

During the polymerization reaction, concomitant use may also be made ofpolar compounds or Lewis bases. Any of the additives known from theliterature for anionic polymerization is in principle suitable. Theadditives generally contain at least one O, N, S or P atom which has afree electron pair. Preference is given to ethers and amines, e.g.tetrahydrofuran, diethyl ether, tetrahydropyran, dioxane, crown ethers,alkylene glycol dialkyl ethers, e.g. ethylene glycol monoethyl ether,ethylene glycol dimethyl ether, N,N,N′,N′-tetramethylethylenediamine,N,N,N′,N″,N″-pentamethyldiethylenetriamine, 1,2-bis(piperidino)ethane,pyridine, N,N,N′,N′,N″,N′-hexamethyltriethylenetriamine, andhexamethylphosphoramide.

The polar compounds or Lewis bases act as an activator and in many casesincrease the conversion in the polymerization reaction or raise thereaction rate. They can also control the proportions of the differentvinyl linkages in the butadiene polymer or isoprene polymer, see below,and thus affect the microstructure of the rubber. If they increase thereaction rate, their amount is advantageously judged so that thereaction rate of the entire mixture is lower than that in a mixturewhich uses no addition of the retarding components. To this end, use ismade of less than 500 mol %, preferably less than 200 mol %, and inparticular less than 100 mol %, of the polar compound or Lewis base,based on the initiator composition.

The process of the invention may be carried out in the presence(solution polymerization) or absence (bulk polymerization) of a solvent.With no solvent, operations are generally carried out at above 100° C.,these being temperatures at which polymer melts may also be handled.

Suitable solvents for the anionic polymerization are the usualaliphatic, cycloaliphatic, or aromatic hydrocarbons having from 4 to 12carbon atoms, for example pentane, hexane, heptane, cyclohexane,methylcyclohexane, isooctane, decalin, benzene, alkylbenzenes, such astoluene, xylene, ethylbenzene, or cumeme, or a suitable mixture. Thesolvent should be of the purity typically required for the process. Toremove substances with active protons, it may be dried over aluminumoxide or molecular sieve, for example, and/or distilled prior to use.The solvent from the process is preferably reused after condensation ofthe solvent vapors and the purification mentioned.

In solution polymerization, operations are usually carried out at from 0to 250° C., preferably from 20 to 200° C.

It is possible to adjust the retardant action within wide temperatureranges via the selection of composition and amount of theorganylaluminum compounds. For example, it is even possible to usestarting monomer concentrations in the range from 50 to 100 percent byvolume, in particular from 70 to 100 percent by volume, for thepolymerization. These give high-viscosity polymer solutions and, atleast for relatively high conversions, demand relatively hightemperatures.

Once the polymerization has ended, the living polymer chains may becapped by a chain terminator. Suitable chain terminators are substanceswith active protons or Lewis acids, examples being water, alcohols, suchas methanol or isopropanol, aliphatic or aromatic carboxylic acids, andalso inorganic acids, such as carbonic acid or boric acid.

The process of the invention may be carried out in any reactor which canwithstand pressure and heat, and in principle it is possible to useback-mixing or non-back-mixing reactors (i.e. reactors with stirred tankbehavior or tubular reactor behavior).

Depending on the selection of the initiator concentration and initiatorcomposition, of the specific process sequence used, and otherparameters, such as temperature and, if desired, temperature program,the process leads to polymers with high or low molecular weight.Examples of suitable equipment are stirred tanks, tower reactors, loopreactors, and also tubular reactors or tube-bundle reactors, with orwithout internals. Internals may be static or movable internals.

Besides the polymerization process described above and the use of theinitiator composition for preparing polymers, the invention alsoprovides the polymers obtainable by the polymerization process.

Examples of these polymers are homopolymers, such as polystyrene (PS orGPPS for general-purpose polystyrene), polybutadiene (PB), andpolyisoprene (PI). Examples of copolymers are high impact polystyrene(HIPS) and styrene-butadiene block copolymers (S-B polymers, which canbe abbreviated to SBP).

The process of the invention therefore permits the preparation ofthermoplastic molding compositions (e.g. PS or HIPS) and of elastomers(e.g. PB, PI, SBP).

The styrene-butadiene block copolymers of the invention may be lineartwo-block S-B copolymers or three-block S-B-S or B-S-B copolymers, forexample (S=styrene block, B=butadiene block), these being obtained viaanionic polymerization by the process of the invention. The way in whichthe block structure arises is essentially that styrene alone is firstpolymerized anionically, giving a styrene block. Once the styrenemonomers have been consumed the monomer is changed by feeding monomericbutadiene and polymerizing this anionically to give a butadiene block(“sequential polymerization”). The resultant two-block S-B polymer maybe polymerized to give a three-block S-B-S polymer by again changing themonomer to styrene, if desired. The same principle applies for B-S-Bthree-block copolymers.

In the three-block copolymers, the two styrene blocks may be of the samesize (same molecular weight, i.e. symmetrical S₁-B-S₁ structure) or ofdifferent size (different molecular weight, i.e. asymmetrical S₁-B-S₂structure). The same principle applies for the two butadiene blocks ofthe B-S-B block copolymers. Block sequences S—S-B or S₁—S₂-B, or S-B-Bor S-B₁-B₂ are, of course, also possible. The indices above representthe block sizes (block lengths or molecular weights). The block sizesdepend on the amounts of monomers used and the polymerizationconditions, for example.

Instead of the elastomeric “soft” butadiene blocks B, or in addition tothe blocks B, there may also be B/S blocks. These are likewise soft andcontain butadiene and styrene, for example randomly distributed or inthe form of a tapered structure (tapered=gradient from styrene-rich tostyrene-poor or vice versa). If the block copolymer contains two or moreB/S blocks, the absolute amounts, and the relative proportions, ofstyrene and butadiene in each of the B/S blocks may be identical ordifferent (giving different blocks (B/S)₁, (B/S)₂, etc.).

Other suitable styrene-butadiene block copolymers are four-block andpolyblock copolymers.

The block copolymers mentioned may have a linear structure (describedabove). However, branched or star-shaped structures are also possibleand are preferred for some applications. Branched block copolymers areobtained in a known manner, e.g. by graft reactions of polymeric “sidebranches” onto a main polymer chain.

An example of a method for obtaining star-shaped block copolymers isreaction of the living anionic chain ends with an at least bifunctionalcoupling agent. Examples of descriptions of these coupling agents arefound in U.S. Pat. Nos. 3,985,830, 3,280,084, 3,637,554, and 4,091,053.Preference is given to epoxidized glycerides (e.g. epoxidizedlinseed-oil or soy oil), silicon halides, such as SiCl₄, ordivinylbenzene, or else polyfunctional aldehydes, ketones, esters,anhydrides, or epoxides. Other compounds suitable specifically fordimerization are dichlorodialkylsilanes, dialdehydes, such asterephthalaldehyde, and esters, such as ethyl formate. Coupling ofidentical or different polymer chains may be used to prepare symmetricalor asymmetrical star structures, i.e. each of the branches in the starmay be identical or different, and in particular may contain differentblocks S, B, B/S, or different block sequences. Further details relatingto star-shaped block copolymers can be found in WO-A 00/58380, forexample.

The monomer names styrene and butadiene used above are given by way ofexample but also include other vinylaromatics and dienes, respectively.

The styrene-butadiene block copolymers are in accordance with theinvention as long as at least one block has been prepared by the processof the invention. This means that it is not necessary for all of theblocks to be prepared by the process of the invention. For example, itis possible for at least one block to be polymerized using an initiatorcomposition of the invention comprising alkali metal hydride andorganylaluminum compound and for one or more other blocks of the sameblock copolymer to be prepared by another process not of the invention,for example using organolithium compounds or organomagnesium compounds.

The high impact polystyrene (HIPS) of the invention comprises, besidesthe polystyrene matrix, a rubber component, such as polybutadiene,polyisoprene, or —preferably—styrene-butadiene block copolymers.

The rubber components here may be prepared by the process of theinvention or else by processes of the prior art, e.g. by anionicpolymerization using organolithium compounds, or by free-radicalpolymerization.

In the case of rubbers prepared by anionic polymerization, the rubber isgenerally present in solution in a solvent or in monomeric styrene. Inthe process of the invention, the rubbers do not need to be removed fromthe solvent (although this is possible). Instead, the solution of therubber with solvent may be used directly for further processing to givethe HIPS.

To this end, monomeric styrene and the initiator composition of theinvention are added to the rubber solution which, where appropriate, haspreviously been permitted to complete its reaction by way of addition ofchain terminator, and the mixture is polymerized anionically by theprocess of the invention, i.e. styrene is polymerized in the presence ofthe rubber.

Polymers of the invention include an HIPS comprising rubber preparedaccording to the invention, where the styrene matrix has beenpolymerized by a process other than the inventive process in thepresence of the rubber.

The HIPS of the invention therefore encompasses HIPS polymers in whicheither the rubber component or the styrene matrix or both constituentshave been prepared by the process of the invention.

According to the invention, particular preference is given toimpact-resistant polystyrene molding compositions in which the rubberpresent comprises

-   a) a styrene-butadiene two-block S₁-B₁ copolymer with styrene    content of from 30 to 70% by weight, preferably from 40 to 60% by    weight, based on the two-block copolymer, or-   b) a mixture of the two-block copolymer described in a) with a    second styrene-butadiene two-block S₂-B₂ copolymer with styrene    content of from 10 to 50% by weight, preferably from 20 to 40% by    weight, based on the two-block copolymer, or-   c) a mixture of the two-block copolymer described in a) with a    styrene-butadiene-styrene three-block S-B-S copolymer with styrene    content of from 5 to 75% by weight, preferably from 20 to 50% by    weight, based on the three-block copolymer. The three-block    copolymer used particularly preferably comprises a S₁-B-S₂ polymer    in which the styrene block S₁ has a weight-average molecular weight    Mw of from 20 000 to 200 000, preferably from 50 000 to 120 000, the    butadiene block B has a Mw of from 30 000 to 300 000, preferably    from 100 000 to 200 000, and the styrene block S₂ has a Mw of from    1000 to 100 000, preferably from 5000 to 30 000.

In the case of the styrene-butadiene block copolymers, in thepolybutadiene, and in the polyisoprene, the process of the inventionmoreover permits control of the content of 1,2-vinyl linkages in thepolybutadiene or polyisoprene. Since the mechanical properties of thesepolymers are also determined by the 1,2-vinyl content of thepolybutadiene or polyisoprene, the process therefore permits thepreparation of polybutadiene, polyisoprene, and styrene-butadiene blockcopolymers with tailored properties.

For example, if —not according to the invention—metallic sodium intetrahydrofuran is used in place of the initiator composition of theinvention, a polyisoprene prepared in this way has high content of1,2-vinyl linkages, giving a different property profile, in particulardifferent mechanical properties.

The polymers of the invention also have low content of residual monomersor residual oligomers. This advantage is particularly significant in thecase of the styrene-containing polymers PS, HIPS, and P-S-B, since thelow content of residual styrene monomers and styrene oligomers makes itunnecessary to carry out any subsequent devolatilization—e.g. in avented extruder, associated with higher costs and disadvantageousthermal degradation of the polymer (depolymerization).

The polymers may comprise conventional additives and processing aids,e.g. lubricants, mold-release agents, colorants, e.g. pigments or dyes,flame retardants, antioxidants, light stabilizers, fibrous andpulverulent fillers, fibrous and pulverulent reinforcing agents, orantistats, or else other additives, or a mixture of these.

Examples of suitable lubricants and mold-release agents are stearicacids, stearyl alcohol, stearic esters, stearamides, etal stearates,montan waxes, and those based on polyethylene and polypropylene.

Examples of pigments are titanium dioxide, phthalocyanines, ultramarineblue, iron oxides, and carbon black, and also the other organicpigments. For the purposes of the present invention, dyes are any of thedyes which can be used for the transparent, semitransparent ornon-transparent coloring of polymers, in particular those suitable forthe coloring of styrene copolymers. Dyes of this type are known to theskilled worker.

Examples of flame retardants which may be used are thehalogen-containing or phosphorus-containing compounds known to theskilled worker, magnesium hydroxide, and other commonly used compounds,or a mixture of these.

Examples of suitable antioxidants (heat stabilizers) are stericallyhindered phenols, hydroquinones, various substituted representatives ofthis group, and also mixtures of these. They are commercially availablein the form of Topanol® or Irganox®, for example.

Examples of suitable light stabilizers are various substitutedresorcinols, salicylates, benzotriazoles, benzophenones, HALS (hinderedamine light stabilizers), for example those commercially available inthe form of Tinuvin®.

Examples which may be mentioned of fibrous or pulverulent fillers arecarbon fibers or glass fibers in the form of glass wovens, glass mats,or glass silk rovings, chopped glass, glass beads, and alsowollastonite, particularly preferably glass fibers. When glass fibersare used, these may have been provided with a size and with a couplingagent to improve compatibility with the components of the blend. Theglass fibers incorporated may either be short glass fibers or elsecontinuous-filament strands (rovings).

Suitable particulate fillers are carbon black, amorphous silica,magnesium carbonate, chalk, powdered quartz, mica, bentonites, talc,feldspar, or in particular calcium silicates, such as wollastonite, andkaolin.

Examples of suitable antistats are amine derivatives, such asN,N-bis(hydroxyalkyl)alkylamines or -alkyleneamines, polyethylene glycolesters, or glycerol mono- and distearates, and also mixtures of these.

Each of the additives is used in the respective usual amounts, and nofurther details need therefore be given here.

The molding compositions of the invention may be prepared by mixingprocesses known per se, for example with melting in an extruder, Banburymixer, kneader, or on a roll mill or calender.

However, the components may also be mixed “cold”, the mixture composedof powder or pellets not being melted and homogenized until processingbegins.

It is preferable for the components, where appropriate with theadditives mentioned, to be mixed in an extruder or any other mixingapparatus at from 100 to 320° C., with melting, and discharged. It isparticularly preferable to use an extruder.

The molding compositions can be used to produce moldings of any type(including semifinished products, films, sheeting, and foams).

The invention therefore also provides the use of the polymers of theinvention for producing moldings, films, fibers, and foams, and themoldings, films, fibers, and foams obtainable from the polymers.

EXAMPLES

1. Preparation of Initiator Compositions

The following compounds were used:

-   lithium hydride (L1H) and sodium hydride (NaH) in solid form from    Aldrich,-   triisobutylaluminum (TIBA) in the form of ready-to-use 1.0 molar    solution in toluene from Aldrich,-   toluene from BASF, purified and dried using aluminum oxide.

General Specification for Examples I1 to I6

The alkali metal hydride (type and quantity, see table 1) was added,with stirring at 25° C., to a 1.0 molar solution of TIBA in toluene(amount of solution, see table 1), and the mixture was stirred at 50° C.for 24 hours after addition of toluene (amount, see table 1). This gavean initiator solution which was used without further treatment. Themolar ratio of aluminum to alkali metal is given in table 1. Operationswere carried out with exclusion of moisture in a glovebox undernitrogen.

TABLE 1 Initiator compositions Alkali metal TIBA Molar ratio Ex. hydridesolution Toluene Al/Li or Al/Na I1 0.8 g LiH 40 ml 960 ml 0.4:1 I2 0.8 gLiH 70 ml 930 ml 0.7:1 I3 0.8 g LiH 90 ml 910 ml 0.9:1 I4 2.4 g NaH 40ml 960 ml 0.4:1 I5 2.4 g NaH 70 ml 930 ml 0.7:1 I6 2.4 g NaH 90 ml 910ml 0.9:12. Polymerization of Monomers

The compounds used were those given under 1 and the following compounds:

-   styrene, isoprene, and 1,3-butadiene from BASF, in each case    purified and dried using aluminoxane,-   sec-butyllithium from FMC,-   methanol and isopropanol from BASF,-   cyclohexane from BASF, purified and dried using aluminoxane,-   tetrahydrofuran (THF) from BASF.

All of the polymerizations were carried out with exclusion of moisturein a glovebox under nitrogen.

The molecular weights given below for the polymers (weight-average M_(w)and number-average M_(n)) were determined by gel permeationchromatography (GPC). The details were as follows: eluenttetrahydrofuran; flow rate 1.2 ml/min; RI or UV detector; threestyrene-divinylbenzene gel separating columns (35° C., each 300×8 mm)Polymer Laboratories PLgel Mixed B; calibration using polystyrenestandards, polyisoprene standards, or polybutadiene standards, dependingon the polymer obtained.

The polydispersity M_(w)/M_(n) was calculated from M_(w) and M_(n).

The styrene content of the rubbers was determined by evaluating ¹Hnuclear magnetic resonance (NMR) spectra. The content of 1,2-vinyllinkages in the polybutadiene, in the polyisoprene, or in the butadienecontent of the styrene-butadiene block copolymer was determined by ¹³Cnuclear magnetic resonance spectroscopy.

2a) Preparation of Polystyrene (PS)

General specification for Examples PS1 to PS9c

One of the initiator solutions prepared previously in examples I1 toI6—or in the case of examples PS8c and PS9c solid initiator—(nature andamount, see table 2) and monomeric styrene (amount, see table 2) wereadded at 100° C. with stirring to 27 ml of toluene. The fall-off instyrene concentration was followed gravimetrically. After a certainreaction time (see table 2) the polymerization was terminated by adding1 ml of methanol. Table 2 includes the conversion achieved at thatjuncture. GPC analysis was used to determine the molecular weights M_(w)and M_(n) of the resultant polymer mixture, and the polydispersityM_(w)/M_(n) was calculated, see table 2.

TABLE 2 Polystyrene (n.d. not determined, c for comparison) InitiatorReaction M_(n) Ex solution* Styrene time Conversion [g/mol] M_(w)/M_(n)PS1 3 ml I1 3.5 ml 5 h 13% 1800 1.3 PS2 3 ml I2 3.5 ml 5 h  8% 1000 1.2PS3 3 ml I3 3.5 ml 24 h  15% 1600 1.1 PS4 3 ml I3 35 ml 260 h  95% 120000 1.2 PS5 3 ml I4 3.5 ml 2 h 82% 6800 1.3 PS6 3 ml I5 3.5 ml 2 h 41%6800 1.3 PS7 3 ml I6 3.5 ml 2 h 20% 2000 1.2 PS8c 0.1 g LiH 3.5 ml 24 h <1% n.d. n.d. PS9c 0.1 g NaH 3.5 ml 24 h  <1% n.d. n.d. * examples PS8Vand PS9V: solid initiator

The examples show that polystyrenes with low polydispersity and“tailored” molecular weights are obtained.

As expected, the conversion within the series PS1 to PS3 and PS5 to PS7reduces as organylaluminum compound content in the initiator compositionrises (molar ratios Al/Li or Al/Na in examples PS1 and PS5, 0.4:1, PS2and PS6, 0.7:1, PS3 and PS7, 0.9:1), since the organylaluminum compoundacts as retarder. (In the case of example PS3, the higher conversion isdue merely to the substantially longer polymerization time, 24 h insteadof 5 h).

Example PS4 differs from example PS3 in the larger amount of monomer andthe longer reaction time. This method can be used to prepare polymerswith high molecular weight.

Comparison of LiH (series PS1 to PS3) with NaH (series PS5 to PS7)reveals that —indeed despite shorter polymerization time—NaH delivershigher conversions and higher molecular weights than LiH.

The comparative examples PS8V and PS9V illustrate that the monomers donot polymerize (no conversion after 24 h) if —not according to theinvention—LiH or NaH is used without organylaluminum compound.

2b) Preparation of Polyisoprene (PI)

General Specification for Examples PI1 to PI3

An initiator solution (nature and amount, see table 3) and monomericisoprene (amount, see table 3) were added, with stirring at 80° C., to27 ml of toluene. The fall-off in isoprene concentration was followedgravimetrically. After a certain reaction time (see table 3) thepolymerization was terminated by adding 1 ml of methanol. Table 3includes the conversion achieved at that juncture. GPC analysis was usedto determine M_(w) and M_(n) for the resultant polymer mixture, and thepolydispersity was calculated, see table 3. ¹³C NMR was used todetermine the proportions of the different vinyl linkages.

TABLE 3 Polyisoprene Initiator Reaction M_(n) Ex. solution Isoprene timeConversion [g/mol] M_(w)/M_(n) Vinyl linkages PI1 3 ml I1 8 ml 7 days 9% 49 000 1.2 0% 1,2-vinyl 90% 1,3-trans 10% 3,4-trans PI2* 3 ml I1 8ml 7 days 76% 47 000 1.2 1.6% 1,2-vinyl 59.6% 1,4-trans 38.9% 3,4-transPI3 2.5 ml I4 8 ml 4 days 70% 46 000 1.3 3.5% 1,2-vinyl 43% 1,4-trans53.5% 3,4-trans * 10 mol eq/Li of THF were also added to the mixture

The examples show that the polyisoprenes have low polydispersity andtailored molecular weights.

When comparison is made with example PI1, addition of THF in example PI2permits the proportions of 1,2-, 1,4-trans, and 3,4-trans linkages to bechanged, and therefore allows control of the microstructure of thepolymer and allows conversion to be increased.

If NaH is used instead of LiH in the initiator composition, higherconversions can be achieved: in example PI3 (using NaH) the conversionis higher, despite considerably shorter polymerization time than inexample PI1 (using L1H).

2c) Preparation of Polybutadiene (PB)

Example PB1

3 ml of the initiator solution I5 and sufficient monomeric butadiene toleave a butadiene concentration of 1 mol/l in the mixture were added at80° C. with stirring to 27 ml of toluene. The fall-off in butadieneconcentration was followed gravimetrically. After a reaction time of 2days the polymerization was terminated by adding 1 ml of methanol. Theconversion achieved was 10%. ¹³C NMR was used to determine 25% of1,2-vinyl linkages and 55% of 1,4-trans linkages.

2d) Preparation of Styrene-Butadiene Block Copolymers (SBP)

General Specification for Examples PSB1 to PSB4

Linear block copolymers were prepared by sequential polymerization ofstyrene and butadiene-styrene mixtures. For this, 500 ml of cyclohexanewas stirred, forming an initial charge. Table 4a gives the initiators,monomers, and temperatures used for each of the blocks. The monomers andinitiators for the next block were not added until the monomers for theprevious block had been consumed. In the case of examples PSB1 and PSB2,the reaction was finally terminated using isopropanol. Table 4b alsoincludes the block structure of the resultant polymers and theproportions by weight of each of the blocks in the block polymer.

In table 4a

-   I5 is initiator solution from example I5-   1 M TIBA is 1.0 molar solution of TIBA in toluene-   B is monomeric butadiene-   S is monomeric styrene-   } is joint addition.

In table 4b:

-   S₁, S₂, S₃ is a styrene block-   (B/S)₁, (B/S)₂ is a butadiene-styrene block.

TABLE 4a Styrene-butadiene block copolymers Ex. PSB1 PSB2 PSB3 PSB4Block 1 Initiator 16 ml I5 16 ml I5 13 ml I5 13 ml I5 Monomers 36 g S 16g S 78 g S 79 g S Temp. 100° C. 100° C. 100° C. 100° C. Block 2Initiator 0.3 ml 1 M 0.3 ml 1 M 45 ml I5 45 ml I5 TIBA TIBA Monomers 23g B 23 g B 46 g S 50 g S {close oversize brace} {close oversize brace}23 g S 23 g S Temp. 120° C. 120° C. 120° C. 120° C. Block 3 Initiator —— 1 ml 1 M 1 ml 1 M TIBA TIBA Monomers 23 g B 23 g B 23 g B 34 g B{close oversize brace} {close oversize brace} {close oversize brace}{close oversize brace} 23 g S 23 g S 23 g S 34 g S Temp. 120° C. 120° C.120° C. 120° C. Block 4 Initiator — — — — Monomers 74 g S 90 g S 26 g S— Temp. 120° C. 120° C. 120° C. —

TABLE 4b Block structure of block copolymers Block structure andproportions by weight of blocks Example in block copolymers [% byweight] PSB1 S₁-(B/S)₁-(B/S)₂-S₂ 18-23-23-36 PSB2 S₁-(B/S)₁-(B/S)₂-S₂8-23-23-46 PSB3 S₁-S₂-(B/S)₂-S₃ 39-23-25-13 PSB4 S₁-S₂-(B/S)₂ 40-26-34

A coupling reaction of the living polymer chains was used to preparestar-shaped block copolymers from the linear block copolymers PSB3 andPSB4, the coupling agent used being epoxidized linseed oil (Edenol® B316from Henkel). The details of the procedure were as in WO-A 00/58380,examples 6 to 8 on pages 8 to 9.

The examples show that tailored styrene-butadiene block copolymers canbe prepared by using appropriate monomer changes and initiators. Theycan be converted to star-shaped polymers.

It is not necessary here for all of the blocks to be prepared by theprocess of the invention. Rather, it is possible for one block to beprepared according to the invention using an alkali metalhydride-organylaluminum compound initiator, but for the other block tobe prepared by other processes.

2e) Preparation of High Impact Polystyrene (HIPS)

The rubber component used comprised styrene-butadiene block copolymersK, these block copolymers K1, K2 and K3 having been prepared usingsec-butyllithium, not according to the invention.

Rubbers K1 and K2: linear butadiene-styrene two-block B-S copolymersdissolved in monomeric styrene

The procedure for K1 was as described in DE-A 100 22 504, example K1 onpage 4, lines 10-25. The procedure for K2 was as described in DE-A 10022 504, example K3 on page 4, lines 42-56. The molecular weights M_(w)for rubber K1 were: polybutadiene block 100 000, polystyrene block 85000, and for rubber K2 were: polybutadiene block 160 000, polystyreneblock 95 000.

Rubber K3: linear styrene-butadiene-styrene three-block S-B-S copolymerdissolved in monomeric styrene

The procedure was as described in DE-A 100 22 504, example K5 on page 5,lines 6-20. The molecular weights M_(w) were: first styrene block 15000, butadiene block 120 000, second styrene block 70 000.

The HIPS was prepared by continuous polymerization, by polymerizingstyrene by the process of the invention in the presence of the aboverubbers K1, K2, or K3, in accordance with the following specification.

Examples HI1 to HI3

Styrene and

-   -   for HI1, 653 g/h of rubber solution K1,    -   for HI2, 661 g/h of rubber solution K2,    -   for HI3, 688 g/h of rubber solution K3        were metered continuously, with stirring, into a 1.9 l stirred        tank at    -   363 g/h for HI1, 380 g/h for HI2, 361 g/h for HI3,        as were    -   initiator 13 for HI1,    -   initiator 16 for HI2,    -   initiator 13 for HI3        at 35 ml/h, and the mixture was held at 90° C. (HI2: 93° C.).        The solids content of the mixture was    -   41% by weight for HI1, 43% by weight for HI2, 40% by weight for        HI3.

The mixture was conveyed onward to a 4 l tower reactor provided with twoheating zones of equal size (internal temperature of first zone 120° C.,second zone 160° C.). The discharge from the reactor was treated with 10g/h of a 10% strength by weight solution of methanol in toluene and thenpassed through a mixer into which 2.5% by weight, based on the reactionmixture, of mineral oil was metered, and finally passed through a tubesection heated to 240° C. Finally, the mixture was depressurized via acontrolled-flow valve into a vacuum vessel operated at 10 mbar. The meltwas discharged using a conveying screw, and pelletized. Conversion wasquantitative.

The polystyrene matrix had a molecular weight M_(w) of

-   -   168 000 for HI1, 163 000 for HI2, 175 000 for HI3        and a polydispersity M_(w)/M_(n) of    -   2.8 for HI1, 2.6 for HI2, 2.7 for HI3.

In all three examples the residual monomer content was <5 ppm of styreneand <5 ppm of ethylbenzene.

Example HI4

Example HI3 was repeated with the difference that initiator I6 was used.

4. Properties of HIPS Polymers Prepared

The HIPS pellets were used to produce pressed test specimens to DIN16770 Part 1 and injection-molded test specimens to ISO 3167.

Yield stress and tensile strain at break were determined to DIN 53455 at23° C.

Surface gloss was determined by measuring gloss with a micro-TRI-glossreflectometer from BYK-Gardner, to give reflectometer values to DIN67530 at observer angle of 60° and 20°.

Hole notch impact strength was determined to DIN 53753 at 23° C. onpressed plaques of 50×6×4 mm with a hole diameter of 3 mm.

The Vicat B heat distortion temperature of the specimens was determinedvia the Vicat softening point. The Vicat softening point was determinedon standard small specimens to DIN 53 460, Method B, using a force of49.05 N and a temperature rise of 50 K per hour.

The flowability of the molding compositions was determined as meltvolume index (MDI) to DIN 53 735 at 260° C. with a load of 5 kg.

Table 5 gives the results.

TABLE 5 HIPS properties (n.d. not determined) Example HI1 HI2 HI3 HI4Yield stress [N/mm²] 32.1 32.5 30.3 29.5 Surface gloss 91/62 n.d. n.d.n.d. [%] at 60°/20° Tensile strain at break [%] 11 23 25 32 Hole notchimpact 4.5 12.6 15.1 14.7 strength [kJ/m²] MVI [ml/10 min] 7.6 6.4 4.85.2 Vicat B [° C.] 89 91 91 90

The examples confirm that polymers with tailored mechanical and thermalproperties can be prepared by the process of the invention.

1. A process for the anionic homo- or copolymerization of styrenemonomers or of diene monomers or mixtures of these in the presence of aninitiator composition, where the initiator composition comprises atleast one alkali metal hydride selected from LiH, NaH, and KH, and atleast one organylaluminum compound, and the molar ratio of aluminum toalkali metal is from 0.01:1 to 5:1.
 2. A process as claimed in claim 1,where triisobutylaluminum is used as organylaluminum compound.
 3. Aprocess as claimed in claim 1, where styrene is used as styrene monomer.4. A process as claimed in claim 1, where butadiene or isoprene or amixture of these is used as diene monomer.
 5. A process as claimed inclaim 2, where styrene is used as styrene monomer.
 6. A process asclaimed in claim 5, where butadiene or isoprene or a mixture of these isused as diene monomer.
 7. A process as claimed in claim 2, wherebutadiene or isoprene or a mixture of these is used as diene monomer. 8.A process as claimed in claim 3, where butadiene or isoprene or amixture of these is used as diene monomer.
 9. An initiator compositionfor anionic polymerization, comprising LiH and at least oneorganylaluminum compound, wherein the molar ratio of Al/Li is from 0.4:1to 0.9:1.
 10. An initiator composition for anionic polymerization,comprising NaH and at least one organylaluminum compound, wherein themolar ratio of Al/Na is from 0.4:1 to 0.9:1.